The invention relates to a lifting apparatus comprising at least two masts and a load engaging mechanism moveable vertically along the masts. More particularly, the invention relates to brake mechanisms for preventing either the operator's cab or the load of such an apparatus from accidentally dropping. Still more particularly, the invention relates to cranes.
A conventional double-masted crane has two masts supported either from above (such as by a trolley moving along a bridge) or from below (such as by a base moving along rails on the ground). An operator's cab is mounted on the masts for housing an operator controlling the crane. A load engaging mechanism, such as a shuttle mechanism or a pair of forks, moves with the cab. The load engaging mechanism is raised and lowered by a hoist assembly.
This type of crane typically includes, on each of the two masts, a brake mechanism for preventing undesirable or uncontrolled downward movement of the operator's cab or the load relative to the masts. A brake mechanism includes a brake member which is supported by a housing mounted on the mast and which engages the mast to prevent downward movement of the cab relative to the mast. An overspeed mechanism causes the brake member to engage the mast when the downward velocity of the cab relative to the mast exceeds a predetermined value.